A hybrid drive unit includes a combustion engine as well as at least one electric machine capable of being operated alternatively as a motor or as a generator. When operated as a motor, the electric machine is powered by an energy storage device and supplies a positive electric motor torque, which together with a combustion engine torque of the combustion engine represents a total drive torque of the hybrid drive unit.
Hybrid vehicles refer to motor vehicles, in which at least two drive sources, which access different energy sources, are combined in order to provide the power for driving the vehicle. The characteristics of a combustion engine, which generates kinetic energy by burning gasoline or diesel fuels, and an electric machine, which converts electric energy into kinetic energy, complement each other. For this reason, current hybrid vehicles are predominantly equipped with a combination of combustion engine and one or multiple electric machines. It is possible to distinguish two different hybrid concepts. In so-called serial hybrid concepts, the vehicle is driven exclusively by the electric machine, while the combustion engine generates, via a separate generator, the electric current for charging an energy storage device that powers the e-machine or for powering the e-machine directly. By contrast, currently, at least in passenger car applications, parallel hybrid concepts are preferred, in which the vehicle may be driven both by the combustion engine and by the e-machine.
Example embodiments of the present invention relate particularly to such parallel arrangements.
The electric machines used in such parallel arrangements may be operated alternatively as a motor or as a generator. In combustion engine propulsion, the e-machine is operated predominantly as a generator, an electric power of the e-machine thus generated being used, for example, to charge the energy storage device and/or to supply a vehicle electrical system. In the case of a power-distributed hybrid arrangement having more than one e-machine, the operation of an e-machine as a generator may also be used to power another. Furthermore, normally at least a part of a braking power is raised by the e-machine operated as a generator (recuperation), a part of the mechanical energy loss being converted into electrical energy. By contrast, when operated as a motor, the e-machine is typically switched on at operating points having higher vehicle loads to support the combustion engine (boost function), e.g., the combustion engine torque and the electric motor torque are added together. In addition, the e-machine may take on the function of a starter motor for the combustion engine. In addition, power-distributed hybrid arrangements are used as well, in which two e-machines and the combustion engine are coupled via a planetary wheel gear and the power flow may also be divided into to electrical and mechanical power. In hybrid arrangements, it is considered advantageous that the e-machines work more efficiently than conventional claw pole generators.
Especially in single-shaft parallel hybrids, the e-machine is normally switched on for support in order to improve the driving performance when engine speeds are low and the driver at the same time makes a high load demand. At high rotational speeds, by contrast, usually no power addition is performed so as not to exhaust the energy storage device and in order to achieve a reproducible vehicle performance independently of the charge state of the energy storage device. Combustion engines having charge-air superchargers, e.g., turbochargers or compressors, normally have a very low specific torque (unit Nm/dm3 displacement) at low rotational speeds, e.g., below 2,000 rpm, whereas high specific torques are achieved in the medium and high rotational speed range. This effect is also referred to as turbo lag. The use of the e-machine as a motor is also used for the purpose of smoothing out this turbo lag. In contrast to naturally aspirated engines, only a low electromotive torque support is required for a harmonic torque characteristic at rotational speeds far above 2,000 rpm.
In supercharged combustion engines, but also in naturally aspirated engines, it is believed to be problematic that the energy storage devices of the electric machines do not provide a uniform charging and discharging capacity across all state ranges. For example, a low charge state (SOC, for state of charge) or an aging (SOH, for state of health) of the energy storage device results in markedly reduced discharging capacities in supplying the electric machine for its operation as a motor. At high load demands, e.g., in the medium rotational speed range, this results in a poorly reproducible total torque and driving performance of the hybrid vehicle.
Example embodiments of the present invention provide a control system for coordinating the torques of the combustion engine and the e-machine, which may provide maximum driving performances, e.g., a maximum torque, while offering the highest possible reproducibility at the lowest possible fuel consumption. Furthermore, a suitable torque control system is to be provided for implementing the method.
In the event that a desired torque is greater than a combustion engine maximum torque, which is optimized for low fuel consumption, the method provides—at least within predetermined rotational speed ranges—for the electric machine to be operated in a supportive manner as a motor having a positive electric motor torque. This means that it is only when a desired torque is demanded by the driver, which exceeds the consumption-optimized maximum torque of the combustion engine, that the electric machine is switched on to produce the high total drive torque. In this context, consumption-optimized combustion engine maximum torque signifies a normally not to be exceeded maximum torque, which may be produced by the combustion engine when this is operated as a function of a current load point having operating parameters (such as ignition point, injection parameters, e.g., also air ratio and others, etc.) that are optimized for a highest-possible efficiency and thus a low fuel consumption. Example embodiments of the present invention may provide for specifying a electric motor maximum torque of the electric machine that is not to be exceeded as a function of at least one state parameter of the energy storage device powering the electric machine. In this manner, a variable electric motor maximum torque is produced, which is adjusted to a current energy storage device state.
Example embodiments of the present invention provide for a maximum total drive torque of the hybrid drive unit, e.g., the maximum total torque to be produced by the sum of the electric motor torque and the combustion engine torque, to be configured, at least in a predetermined rotational speed range, substantially for a consumption-independent combustion engine maximum torque of the combustion engine. In contrast to the consumption-optimized torque, the consumption-independent (or consumption-ignoring) combustion engine maximum torque corresponds to a maximum torque producible by the combustion engine alone without regard to an increased fuel consumption. For example, the maximum total drive torque of the hybrid drive unit is preset, e.g., to at least 90%, e.g., to at least 95% of the consumption-independent combustion engine maximum torque. At least in the predetermined rotational speed range, this results in a differential torque between the consumption-optimized and the consumption-independent combustion engine maximum torque, which is produced as a function of the state of the energy storage device either by the electric machine (when the energy storage device state is optimal) or by the combustion engine (when the energy storage device is in the worst possible state). In intermediary states of the energy storage device, this differential torque is produced by an appropriate combination of electric motor torque and combustion engine torque. In this manner, a constant maximum total torque and thus a very reproducible vehicle performance may always be ensured. The specified rotational speed range may correspond to rotational speeds above 1,600 rpm, e.g., above 1,800 rpm, e.g., above 2,000 rpm. In supercharged engines, e.g., the so-called turbo lag is substantially completely compensated by an electric motor torque below the specified rotational speed threshold.
A possible state parameter of the energy storage device may be any variable that influences a charging and/or discharging capacity of the energy storage device. In this instance, there is a provision that, if the at least one state parameter corresponds to a decreasing charging and/or discharging capacity, then the specified electric motor maximum torque of the electric machine is lowered accordingly. Such suitable state parameters include a charge state (SOC), an aging state (SOH), an energy storage device temperature (TE) and/or a structure-borne noise excitation of the energy storage device, etc. Therefore, the maximum electric motor torque may be lowered with a decreasing charge state, an increasing aging state, very high or very low energy storage temperatures and/or a strong structure-borne noise excitation, etc. For this purpose, either corresponding threshold values may be specified, or the electromotive maximum torque may be varied proportionally with the mentioned variables.
If the desired torque is greater than a sum of the consumption-optimized combustion engine maximum torque and the variable electric motor maximum torque, then the combustion engine is operated at a torque which is greater than the consumption-optimized combustion engine maximum torque (but smaller than its consumption-independent maximum torque). For this purpose, it may be provided to adjust at least one operating parameter of the combustion engine with respect to its optimum efficiency setting. In other words, independently of the fuel consumption, the combustion engine has operating parameters applied to it that are optimized for a maximum torque. For this purpose, for example, the ignition angle, injection quantity, injection point, air ratio, control times of the intake and/or outlet valves, etc., may be adjusted. Moreover, it is also possible to adjust parameters that affect the type of the air-fuel charge in the combustion chamber of the engine. For example, the position of a charge movement valve arranged in the intake pipe may be influenced. In the case of compressor engines that have a compressor drive having a variable transmission ratio, the transmission ratio may be increased as long as the maximum rotational speed of the compressor is not exceeded. Since the drive power of the compressor rises disproportionately with the rotational speed, this measure is also not optimal as regards consumption, but it results in a higher torque.
Example embodiments of the present invention related to a hybrid drive unit, which has a torque control system that implements the described method steps. The torque control system may also be integrated into a conventional engine control unit and may exist in the form of a program algorithm for implementing the method.
The combustion engine may be a supercharged engine, which is supplied with compressed charge air via a charge air supercharger, e.g., an exhaust gas turbocharger or a variable compressor.
According to an example embodiment of the present invention, a method for controlling torque of a hybrid drive unit including a combustion engine and at least one electric machine operable alternatively as a motor or a generator, includes: powering the electric machine by an energy storage device to operate the electric machine as a motor and supplying a positive electric motor torque together with a combustion engine torque of the combustion engine to produce a total drive torque of the hybrid drive unit; and if a desired torque is greater than a consumption-optimized combustion engine maximum torque, operating the electric machine as a motor having an electric motor torque. An electric motor maximum torque is predetermined as a function of at least one state parameter of the energy storage device.
A maximum producible total drive torque of the hybrid drive unit, at least in one predetermined rotational speed range, may match a consumption-independent combustion engine maximum torque of the combustion engine.
The predetermined rotational speed range may include rotational speeds above 1,600 rpm.
The predetermined rotational speed range may include rotational speeds above 1,800 rpm.
The predetermined rotational speed range may include rotational speeds above 2,000 rpm.
The electric motor maximum torque may be predetermined as a function of the at least one state parameter such that the electric motor maximum torque decreases with decreasing at least one of (a) charging and (b) discharging capacity of the energy storage device.
The at least one state parameter of the energy storage device may include at least one of (a) a charge state, (b) an aging state, (c) an energy storage device temperature and (d) a structure-borne noise excitation of the energy storage device.
The electric motor maximum torque may lower with at least one of (a) a decreasing charge state of the energy storage device, (b) an increasing aging state of the energy storage device, (c) in the event of one of (i) very high and (ii) very low energy storage device temperatures and (d) strong structure-borne noise excitation.
The combustion engine may be operated having a combustion engine torque greater than the consumption-optimized combustion engine maximum torque if the desired torque is greater than a sum of the consumption-optimized combustion engine maximum torque and the electric motor maximum torque.
The method may include adjusting at least one operating parameter of the combustion engine with respect to an efficiency-optimized setting to operate the combustion engine having a combustion engine torque greater than the consumption-optimized combustion engine maximum torque.
The at least one operating parameter of the combustion engine may include at least one of (a) ignition angle, (b) injection quantity, (c) injection point, (d) air ratio, (e) valve timing, (f) charge-influencing parameters and (g) a transmission ratio of a variable compressor.
According to an example embodiment of the present invention, a hybrid drive unit includes: a combustion engine; at least one electric machine configured to operate alternatively as a motor or as a generator; an energy storage device configured to power the electric machine to operate the electric machine as a motor to supply a positive electric motor torque together with a combustion engine torque of the combustion engine to produce a total drive torque of the hybrid drive unit; and a torque control device configured to operate the electric machine as a motor having an electric motor torque if a desired torque is greater than a consumption-optimized combustion engine torque. An electric motor maximum torque is a function of at least one parameter of the energy storage device.
The combustion engine may include a compressed charge air supply device.
The combustion engine may include at least one of (a) a turbocharger and (b) a compressor.
According to an example embodiment of the present invention, a torque control device includes: an arrangement configured to perform a method for controlling torque of a hybrid drive unit including a combustion engine and at least one electric machine operable alternatively as a motor or a generator. The method includes: powering the electric machine by an energy storage device to operate the electric machine as a motor and supplying a positive electric motor torque together with a combustion engine torque of the combustion engine to produce a total drive torque of the hybrid drive unit; and if a desired torque is greater than a consumption-optimized combustion engine maximum torque, operating the electric machine as a motor having an electric motor torque. An electric motor maximum torque is predetermined as a function of at least one state parameter of the energy storage device.
Example embodiments of the present invention are described in more detail below with reference to the appended Figures.